This is my entry for the 3DPrintingNerd challenge. It is designed in Autodesk Inventor. Additional I made a stress analysis with pretty good results. I tested the spool holder with three different forces (all 50N). They simulate two cases.
At first the assembly. You can clamp the holder easily on the wooden bar. I was a bit confused because 3/4 inch were 19,05 mm according to my calculator. In the drawing of the 3DPrintingNerd it was dimensioned with 18mm but it should be fine now. During the assembly the rear part gets bend a bit therefore I would recommend to print it in PETG. Nevertheless, it is reinforced.
The second case is the actual use of the spool holder. The force of the spool is orientated with the gravity. The stress in the holder at 50N (≙ > 5kg of spool weight) still has a minimum safety factor of 4,2 at the back and 6,08 in the front.
You can remove the holder by bending back the little notch and simply taking it off.
I hope someone can use this holder and it will come in handy.